Introduction

Lateral ankle sprain (LAS) is a common injury in sport1. Although most LAS cases are given minimal healthcare concern, some 32-74% demonstrate recurrent onset of ankle sprains or residual chronic symptoms of instability2,3. These musculoskeletal disorders resulting from LAS has been defined as chronic ankle instability (CAI), a condition which may lead to serious economic and medical burdens. Consequently, CAI has received increasing research attention in efforts to explore strategies for effective management.

It has been well-established that dynamic balance deficit is one of the main functional impairments associated with CAI4. The underlying mechanisms for balance deficits in CAI have been ascribed to lower limb muscle weakness and impaired ankle proprioception4. To restore lower limb balance performance, extensive neuromuscular control training programs have been incorporated into CAI rehabilitation protocols5. A number of clinical practice guidelines have provided robust evidence on active exercise-based programs in improving balance performance in the CAI cohort, yet application and clinical effectiveness can be compromised in practice due to the prolonged intervention duration and compliance problems6,7,8,9. In terms of passive interventions for CAI, ankle taping may be a viable therapeutic option due to its cost-effectiveness, availability, and most importantly, minimal interruption of the users’ daily routines and physical activities. The underlying mechanism of ankle taping remains unclear, but it has been thought to assist in preventing excessive ankle movement and augmenting mechanical stimulation to the proprioceptors around the ankle and foot region in such a way as to enhance proprioceptive feedback, which in turn may contribute to ankle stability and improved lower limb functional performance10,11.

Researchers have investigated the effects of kinesiology taping (KT) on proprioceptive performance in both healthy and pathological populations, and the results have shown the therapeutic effect of KT taping to be subject to multiple factors, such as the selection of taping technique, various tensions imposed in KT taping, and perceived comfort level12,13,14. In our recent work we examined the effects of KT taping with different strip lengths on ankle proprioception, and found that the longer KT tape strips could significantly improve ankle movement discrimination sensitivity during landing in individuals with CAI10. In addition, the acute effect of KT taping on dynamic balance was explored and it was found that KT taping can immediately improve dynamic balance in individuals with CAI15. Balance disorders may be associated with proprioceptive deficits4, although some studies have shown contradictory results about this relationship with regards to a possible KT effect, which may be influenced by many factors such as variety among participants11,16, KT length and assessment methods17,18. Our previous study pointed out that longer KT provides better proprioceptive improvement, however, it is unknown whether longer KT also provides better balance improvement in individuals with CAI. Therefore, the study of the effect of different lengths of KT on dynamic balance control still has value.

This study aimed to investigate and compare the effects of KT taping with different strip lengths on dynamic balance in individuals with and without CAI. Lower limb dynamic balance may be related to lower limb muscle strength level19, with moderate tension KT taping activating muscles12 and therefore expected to improve dynamic balance performance. Also, dynamic balance deficits in CAI individuals could be due to proprioceptive impairment. Given that taping with longer strips could lead to greater proprioceptive improvement10 and provide greater wrap coverage on the lower limb region, we hypothesized that in a CAI cohort, long KT taping would provide greater balance performance improvements compared to the improvement obtained with relatively shorter KT taping. In addition, previous work has suggested that ankle KT taping improves ankle proprioception primarily in individuals with lower baseline performance, rather than those with higher baseline performance (Long et al., 2017). Accordingly, the secondary hypothesis of this study was that KT taping would improve dynamic balance performance only in individuals with CAI and not in those without CAI.

Method

Participants

This was a between-groups comparison, repeated-measures trial, with a 24-hour wash-out period between the randomly-allocated repeated-measures conditions. This study was approved by the local Ethics committee (approval number: 102772020RT011). Individuals from a university physical therapy course with and without CAI were to be recruited in this study. Sample size estimation was undertaken using G*power software, with an effect size of 0.25, a power of 0.9, and a significance level of 0.05. It showed that at least 30 participants should be included. Accordingly, sixteen participants with CAI and 15 without CAI were recruited (non-CAI group), with their demographic information is detailed in Table 1. All participants were informed of the content before the experiment, as well as they signed written informed consent. All experiments were performed in accordance with relevant guidelines and regulations.

Table 1 Participant demographics and baseline information.
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As per the selection criteria recommended by the International Ankle Consortium, the eligible participants in the CAI group met the following inclusion criteria20: (1) a history of at least one significant unilateral ankle sprain in the past two years, (2) a history of at least 2 episodes of the ankle joint “giving way” and/or feeling unstable, and (3) a score of ≤ 24 on the Cumberland Ankle Instability Tool (CAIT). The inclusion criteria for the non-CAI group included (1) in a good general health; (2) no history of musculoskeletal injuries that may affect locomotor functioning, (3) score of more than 25 on the CAIT. Participants were excluded if they had any following20: (1) previous lower extremity surgeries, or (2) acute lower limb injuries that led to pain or swelling (nonunion of lower limb fracture, etc.), or (3) severe skin disease, unhealed scar, or allergy to the KT that would have affected the test, or (4) had an ankle sprain within the 3 months before testing.

Taping procedure

Eligible participants were administered the KT taping technique at three different lengths for the involved side in the CAI group, and for the dominant side in the non-CAI group. A modified taping technique21 was utilized to perform above-ankle KT taping (short taping), that is, only the foot and ankle complex region was wrapped by the strip of KT tapes; below-knee KT taping (mid taping), and above-knee KT taping (long taping) (Fig. 1, from left to right, the short, mid and long taping, respectively). Each participant was prepared with skin sterilization to the relevant leg regions prior to KT taping, and then was taped with four strips of KINDMAX 5 cm-width KT tapes in different colors. The first strip, colored green, started from the first cuneiform and first metatarsal bones on the dorsum of the foot and extended upwards along the anterior tibia muscle. The second strip, colored blue, started from first metatarsal and passed laterally around the lateral malleolus and extended upwards along the peroneus longus muscle. The third strip, in red, started from the medial malleolus, and extended posteriorly to the posteromedial aspect of the tibia and fibula. The fourth strip, in black, started from the anterior side of the lateral malleolus, and extended under the plantar surface, pulling up the transverse arch of the foot. Each strip was stretched approximately to 20–35% on its length12,21, without stretch either on the anchors at the start or the end. All the KT application procedures were performed by the same qualified therapist.

Fig. 1
figure 1

Different ankle taping techniques. (a) Short taping. (b) Mid taping. (c) Long taping.

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Outcome measures

In this comparative, repeated-measures trial, all participants were assessed barefoot at the enrollment conducted 24 h prior to taping, then re-assessed immediately after taping. Given the three taping conditions, each participant thus underwent four assessment sessions in total (Fig. 2). The procedural details were as follows:

Fig. 2
figure 2

Study flowchart and participants allocation. CAI chronic ankle instability.

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Dynamic balance was measured using the Y-Balance Test kit (YBT) (Move2Perform, Evansville, IN)22,23. The YBT comprised of a stand platform in the center, three reaching arms equipped with carriages, set at an angle of 120° to each other, corresponding to anterior (YBT-A), posteromedial (YBT-PM), and posterolateral (YBT-PL) directions, respectively (Fig. 3). Prior to formal conduct of the YBT, participants were instructed to stand in barefoot on the stand platform, with both arms akimbo to control trunk displacement, and then instructed to use the uninvolved lower limb to reach and then push outwards the indicator on each metal arm, as far as possible along its longitude axis, while maintaining unipedal balance on the involved limb. A successful test would be when participants could take the reaching leg back steadily from the farthest position on each reaching arm to the stand platform, without losing their original foot position or balance on the tested side. Each participant was offered up to three trials for each reaching arm to accustom them with the procedure, and then was required to complete three trials along the three reaching arms, in a random order. A 3-min rest was provided as needed between trials. The readings on the farthest position attained across the three trials were averaged, then normalized via dividing by the length of the reaching limb to represent the recorded reaching distance on each direction. Lower limb length was measured from the most prominent aspect of the anterior-superior iliac spine to the distal tip of the ipsilateral medial malleolus in supine position23. Finally, a YBT comprehensive score (YBT-C) was calibrated for further analysis based on the average of the normalized reaching distances achieved on the three reaching directions. The computing equation employed was as below:

$$\:Normized\:reaching\:distance\:\left(normAnt,normPM,normPL\right)=\frac{Mean\:of\:the\:three\:reaching\:trials\:\left(cm\right)}{Tested\:limb\:length\:\left(cm\right)}\times\:100$$
$$\:YBT\:comprehensive\:score=\frac{normAnt+normPM+normPL}{3}$$
Fig. 3
figure 3

Y-balance test. (a) Anterior. (b) Posteromedial. (c) Posterolateral.

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Statistical analysis

All statistical analysis was performed using IBM SPSS Statistics 26 software. The significance level of all analyses was set at p<0.05. The Shapiro-Wilk test was performed to test data for normality prior to formal statistical analysis. Independent t test and Chi-square tests were performed to examine the comparability of participants’ demographic scores. Linear mixed model (LMM) analysis was performed to analyze the main effects and interactions between the KT length and Group (CAI and non-CAI) independent variables for the YBT comprehensive score as well as scores in each direction of the YBT. When there was any significant main effect or interaction effect, post hoc tests were applied via pairwise comparisons using Student’s t tests to examine the specific inter-group difference and pre-post changes under each taping condition. Partial eta square(ηp2) was calculated when statistical significance occurred and then used to represent the effect size (ES). As per the rule of thumb introduced by Cohen24, a partial η2 value of 0.01 or less is considered as a small effect size, 0.06 as medium, and 0.14 or higher as large.

Results

The CAI and non-CAI groups were matched in terms of gender ratio, age, height, and body weight (all p>0.05). Non-CAI participants consistently outperformed CAI in CAIT scores (t = 9.66, p = 0.000) and all YBT measures made in the untaped condition (all p<0.05). Sexes have no effect on the pretest assessments (F (1, 27) = 1.529, p = 0.227). LMM analysis suggested that there were significant KT-Group interactions reflecting reducing inter-group difference as tape length increased for YBT-C (F (3, 29) = 5.599, p = 0.016, ES = 0.104), YBT-PM (F(3, 29) = 3.53, p = 0.018, ES = 0.102) and YBT-PL (F(3, 29) = 2.72, p = 0.049, ES = 0.008), but not YBT-A (F(3, 29) = 1.44, p = 0.236). Subsequently, LMM analysis was conducted again for each group (i.e. CAI, non CAI), which suggested that CAI participants showed KT main effects for YBT-C (F(3, 15) = 6.42, p = 0.001, ES = 0.286), YBT-PM (F(3, 15) = 10.06, p = 0.001, ES = 0.386) and YBT-PL (F(3, 15) = 5.23, p = 0.004, ES = 0.265), whereas no KT main effects exhibit for non-CAI group. To further determine the source of the effects of KT in CAI group, paired t-tests was used and suggested compared to the untaped condition, YBT-PM increased in all taping conditions, with mean difference (MD) from 3.5 to 7.0% (t = 2.17–5.17, p = 0.00-0.046, 95%CI = -9.83, -0.07), whereas YBT-C (MD = 4.2%, t = 1.03, p = 0.001, 95%CI = -6.36, -1.97) and YBT-PL scores (MD = 5.3%, t = 3.9, p = 0.001, 95%CI = -8.18, -2.41) increased only in the long-taping condition (Table 2; Fig. 4).

Table 2 Dynamic balance performance in different taping conditions.
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Fig. 4
figure 4

Dynamic balance performance for individuals with CAI and non-CAI under different taping conditions. (a) YBT-C. (b) YBT-A. (c) YBT-PM. (d) YBT-PL. *P < 0.05 indicative of statistical significance. YBT-C Y-balance test – comprehensive score, YBT-A Y-balance test – anterior score, YBT-PM Y-balance test – posteromedial score, YBT-PL Y-balance test – posterolateral score.

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Discussion

The main purpose of this study was to explore the effect of varied strip-lengths of KT on lower limb dynamic balance control in individuals with and without CAI. In line with our hypothesis, there were two main findings: firstly, the KT taping did lead to improved dynamic balance performance in the CAI cohort, but the non-CAI cohort may not benefit from this technique; secondly, that long-strips in KT taping showed the optimal effect, leading to improved reaching performance in YBT-C, YBT-PM and YBT-PL, in contrast to the relatively short tape strips, which only did in YBT-PM.

Overall, the current results suggest that KT taping can improve lower limb dynamic balance in individuals with CAI. Specifically, KT taping can significantly improve reaching performance in YBT-PM and YBT-PL, but not in YBT-A. As indicated by Picot et al.25, the minimum measurable changes of YBT composite scores, PM, and PL should be more than 2.44%, 3.20%, and 3.20%, respectively. The resulting changes in this study all exceeded these reference values (YBT composite scores: 98.0% vs. 93.8%, YBT-PM:112.3-115.8% vs. 108.9%, YBT-PL: 113.2% vs. 107.9% in YBT-PL), compared to the untaped condition, which suggests that the post-intervention effect resulted from KT taping, rather than measurement errors associated with the instrument itself. The YBT is one of the popular variants derived from the star excursion balance test, both of which are frequently used to assess dynamic balance in clinical and laboratory settings, and are capable of identifying lower limb musculoskeletal disorders22,26. Although the discriminative capability of the YBT has been criticized for contradictory findings27,28, partially due to the varied normalization procedures and selection bias, the inter-group difference in YBT performance observed in this study has extended the finding regarding the therapeutic effectiveness of different strip-lengths of KT tape in a CAI cohort, by using a healthy cohort as a reference.

The main contributors to dynamic balance performance can vary in each reaching direction of the YBT. One possible reason as to why KT taping cannot improve the YBT-A performance may be that the YBT-A performance is associated with ankle dorsiflexion range of motion29 and this could explain up to 24% variation of the distance reached, whereas the working mechanism of KT taping has been argued to amplify proprioceptive stimulation30. Posterior reaching distance has shown correlations with lower limb position sense31. Recent work by Shao et al.27 suggested that overall YBT performance demonstrated moderate a correlation with ankle discrimination sense in a mixed cohort involving individuals with and without CAI. In this study, the included individuals who were both with and without CAI showed significant inter-group differences in each reaching distance and composite scores tested in barefoot.

On the other hand, non-CAI group did not improve their lower limb dynamic balance performance, regardless of different KT taping conditions. In line with this observation, one influential work previously conducted by Nakajima et al.32 has reported that in a healthy non-injury young cohort, KT taping did not result in significant change in vertical jumping and SEBT performance. One explanation for this may be that, for healthy individuals with better YBT performance, additional sensory input does not help promoting neuromuscular control. Cumulatively, these different observations support the clinical application of KT taping in the clinical management of CAI, but the KT technique may offer limited benefits for enhancing functional performance in those with stable ankles.

In addition, there were two main findings in terms of the effects of the KT taping technique with different strip lengths on dynamic balance performance in the CAI cohort. Firstly, whichever strip lengths were used in the KT taping, YBT-PM performance showed consistent improvements. Secondly, it was found that a long KT taping showed multidirectional increase in YBT performance, whereas the two relatively short tape strips only did in YBT-PM. This finding supported and extended a previous work in which long-strips of KT taping showed optimal improvement on ankle movement discrimination scores in a CAI cohort10. We speculate that these significant KT intervention changes may be ascribed to a combination of sensory stimulation and mechanical support. As suggested by previous research12, a tension of less than 25% was found to be able to decrease tactile sensitivity, whilst a higher tension was considered to function akin to rigid tape or ankle brace, with pure mechanical support. In comparison, a Jackson method, as used in this study, involved an elastic fixation of the hindfoot by applying a moderate tension (25 ~ 35%). Previous researchers have pointed out that a CAI cohort showed seemingly abnormal motor control throughout the whole lower limb kinetic chain33, and accordingly proposed the need for a comprehensive intervention to be prescribed in this cohort, rather just targeting the involved ankle region. We argue that the cutaneous coverage of a long KT taping technique could not only involve the ankle region but also may integrate with the knee joint to participate in exercising balance of the lower limbs, so it may result in enhanced improvements in functional performance34. The short and mid-length KT taping in this study showed the same effect on the improvement of dynamic balance only in the YBT-PM direction, but not in the comprehensive scores or other directions, where there was an apparent but not significant decrease, suggesting the limitations of passive support interventions or preventive measures applied below the knee in clinical practice. This situation warrants future research to identify the underlying mechanism and work out the optimal parameters for the application of KT taping in CAI cohorts. Nevertheless, the current finding suggests that long kinesiology taping above the knee may yield better effects in improving balance in individuals with CAI. In the prevention and rehabilitation of CAI, there is importance regarding the comprehensive integration of the other joints in the lower limbs besides the ankle joint.

There were some limitations in this study. Firstly, a carry-over effect after each KT taping condition might exist, given a relative short wash-out period (24 h) used in this study. Jackson et al. found that the effect of KT taping was maintained for 72 h after continuous use for 48 h21. However, in this study, the KT tape was removed immediately after each assessment, so we argue that the potential carry-over effect would be limited. Second, a total of four YBT tests were assessed, so there may have been a learning effect for those participants whose last test in the random order was after long taping, although we inserted a 24-hour wash-out interval. In addition, gender differences were not able to be analyzed, due to the relatively small sample size recruited for this study. Previous researchers have found that healthy females tended to benefit more from application of the KT taping technique32, so it awaits future work to identify whether KT taping could act differently between female and males with CAI. Further, YBT assessment of dynamic balance is associated with lower limb muscle strength levels19. In future, it would be useful to explore how the long KT taping provides participants with more stable “mechanical fixation” to support the other leg to move further, and how these potential mechanisms are related to lower limb muscle strength.

Conclusion

KT taping can improve lower limb dynamic balance for individuals with CAI to a level of those without CAI. Long-strips of KT tape tend to show optimal effects, compared to short or mid ones. However, individuals without CAI may not benefit from KT taping. The current findings support the application of KT taping to restore lower limb dynamic balance function for individuals with CAI.